This invention relates to auxiliary vehicle heaters and, in particular, to gear pumps used in conjunction therewith.
Auxiliary vehicle heaters are heaters which are independent of the conventional heaters used in vehicles which are actually heat exchangers transferring heat from the engine coolant. Auxiliary vehicle heaters are usually powered by fuel drawn from the conventional fuel tank of the vehicle. These heaters have a fuel nozzle associated with a burner and a combustion chamber. A fuel pump conventionally draws the fuel from the fuel tank and supplies it to a nozzle of the burner.
In conventional units, fuel is supplied at a relatively high pressure to the nozzle. The pumps are designed so they have the capacity to initially suck the air and lift the fuel from the fuel tank. This requires a relatively high displacement pump. The priming operation requires 8 to 10 times the capacity of pump needed to deliver fuel during normal heater operation. Excess fuel from the fuel pump is returned to the vehicle fuel tank by a fuel return line. Such a fuel return line is disadvantageous for a number of reasons, chiefly the hazard of fuel spillage should the return line be damaged. Also the incorporation of the return line increases the costs and complexity of an auxiliary heater installation.
High pressure fuel systems are, by their nature, prone to fuel leaks through the shaft seal of the pump, through the relief seal, solenoid seal and nozzle seal. Fuel cannot be recirculated within the fuel pump of high pressure fuels systems because of the detrimental effects of large pressure changes. Thus high pressure systems require a fuel return line and draw as much as ten times the fuel required by the burner. They require a large supply line and an additional pressurized return line and associated systems. These relatively complicated installations therefore have a potential for fuel leaks.
Accordingly, there is a need for of fuel supply system for auxiliary vehicle heaters which overcomes these disadvantages.
It is therefore an object of the invention to provide an improved fuel delivery system for auxiliary vehicle heaters which significantly reduces the risks of fuel spillage associated with conventional high pressure systems.
It is another object of the invention to provide an improved fuel delivery system for auxiliary vehicle heaters which eliminates the high flow rates associated with prior art units.
It is further object of the invention to provide an improved fuel delivery system which eliminates the need for a fuel return line extending from the pump to the fuel tank of vehicle.
It is also an object of the invention to provide an improved fuel delivery system for auxiliary vehicle heaters which is simpler and more robust than conventional high pressure systems.